1. Field of the Invention
The present invention relates to a multi-band antenna for tablet computers, especially to a multi-band antenna for tablet computers that covers the GSM850/900/1800/1900/UMTS and LTE700/2300/2700 operations. The multi-band antenna has higher practical value and more applications.
2. Description of Related Art
Along with fast progress in information and communication technologies, people have more requirements for wireless communication technology, not only the quality but also the speed. There are various systems for electronics with communication receivers. The antenna systems of the electronics are not compatible due to different system operation frequencies.
Refer to Taiwanese Pat. App. Pub. No. 201123617 published on Jul. 1, 2011, a multi-band antenna is revealed. The multi-band antenna includes an antenna body, a flat substrate, a grounding part and a feed point. The multi-band antenna is a three-dimensional structure having a bottom surface, a rear surface, a top surface and an outer surface. The above four surfaces are respectively disposed with the antenna body. The flat substrate and the grounding part are arranged at the bottom surface of the multi-band antenna. The flat substrate is located on a gap between the grounding part and the antenna body on the bottom surface of the multi-band antenna. The antenna body, the flat substrate and the grounding part are connected at the feed point.
Refer to Taiwanese Pat. App. Pub. No. 201021292 published on Jun. 1, 2010, a multi-band antenna is revealed. The multi-band antenna includes a loop microstrip line and a parasitic microstrip line. The loop microstrip line consists of a signal feed end and a first grounding end. The length of a path between the signal feed end and the first grounding end is a half wavelength. A signal is input through the signal feed end to excite a first resonant mode frequency from the loop microstrip line. The parasitic microstrip line is composed of a second grounding end and a first open end. The length of a path between the first open end and the second grounding end is one-fourth wavelength. The loop microstrip line is arranged around the parasitic microstrip line. Electromagnetic radiation with the first resonant mode frequency is coupled to the parasitic microstrip line so that the parasitic microstrip line is excited to have a second resonant mode frequency. The second resonant mode frequency is different from the first resonant mode frequency.
However, although the antennas mentioned above perform the expected functions while being applied to multiple system band frequencies, they still have certain limitations. In practice, LTE (Long Term Evolution), a next-generation wireless broadband technology, has been developed. Compared with GSM, the LTE provides higher data speed and a lot better quality. LTE standard can be used with many different frequency bands including 700, 2300, 2500 MHz. Yet GSM-850/900/1800/1900 MHz and UTMS bands are still in use. The above antennas are unable to be used for a broad range of frequencies including LTE700/2300/2500, GSM 850/900/1800/1900, UMTS, etc and there is room for improvement.